Method and apparatus for treating tissues with hifu

ABSTRACT

A method for treating a desired volume of tissue using HIFU or other energy modality to ablate a pattern of elemental treatment volumes each having a volume that is greater than that of the focal zone of the HIFU transducer but smaller than the overall volume of the desired treatment volume. In one embodiment, the pattern of elemental treatment volumes are arranged to form a shell which partially or wholly encapsulates the desired volume of tissue, which then necroses in situ due to effects other than direct HIFU damage (including some combination of ischemia, thermal conduction, inflammation, apoptosis, etc.). The necrosed tissue remains in the body and is subsequently resorbed and/or healed via normal body mechanisms.

RELATED APPLICATION

This application claims the benefit under 35 U.S.C. Section 119(e) ofU.S. Provisional Application 61/102,804 filed Oct. 3, 2008, which isherein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The technology disclosed herein relates to methods and apparatus for thetreatment of internal body tissues and in particular to the treatment ofinternal body tissues with high intensity focused ultrasound (HIFU).

BACKGROUND

There are numerous techniques that are currently used for the treatmentof internal body tissues. For example, internal cancerous andnon-cancerous tumors can be treated with a variety of techniques such assurgery, radiation and chemotherapy. Each of these techniques offersadvantages and disadvantages. One promising non-invasive technology fortreating internal body tissues is high intensity focused ultrasound(HIFU). With HIFU, high intensity ultrasound energy is focused at adesired treatment volume. The energy causes tissue destruction via boththermal and mechanical mechanisms.

One of the drawbacks of using HIFU to treat internal body tissues is thetime required to treat a given volume of tissue. Currently proposed HIFUprocedures may take up to 3 hours to treat a single tumor, which hascontributed to poor acceptance of these procedures by both physiciansand patients. In addition, the amount of energy required to completelyablate a large volume of tissue results in substantial thermalconduction outward from the ablation volume, which can raise the risk ofthermal damage to surrounding healthy tissue.

Given these problems, there is a need for a method of treating internalbody tissues in a manner that reduces treatment time, while improvingboth effectiveness and ease of use, and reducing total required energydeposition.

SUMMARY

To address the problems discussed above, the technology disclosed hereinrelates to a method of treating a desired volume of internal bodytissues with energy from an energy source, which may include highintensity focused ultrasound (HIFU). Such energy sources could alsoinclude radiofrequency, radiation, microwave, cryotherapy, laser, etc.However the preferred embodiment is HIFU, due to its unique ability tobe non-invasively focused deep inside body tissues without the need forpunctures or incisions.

In one embodiment, a desired target volume of tissue is treated withHIFU by ablating a number of adjacent elemental treatment volumes toform “building blocks” used to treat the full target volume of tissue.Each elemental treatment volume is created by directing the focal zoneof a HIFU transducer to ablate a sub-volume that is larger than thefocal zone itself but smaller than the overall desired treatment volume.Each elemental treatment volume is created by repeatedly directing thefocal zone of the HIFU transducer over the perimeter of the elementaltreatment volume as treatment energy is being applied.

In one embodiment, a mechanical or electronic steering apparatus directsthe focal zone of a HIFU beam around the perimeter of the elementaltreatment volume until the tissue encompassed by the perimeter isablated. In one embodiment, a center region of the elemental treatmentvolume is not directly ablated but is treated by thermal conduction asthe perimeter is ablated.

In one embodiment, the disclosed technology includes a HIFU transducerthat is configured to deliver treatment energy to a focal zone and acomputer controlled beam steerer for repeatedly positioning the focalzone over a perimeter of an elemental treatment volume as treatmentenergy is applied.

In one embodiment, a pattern of elemental treatment volumes is createdto form a shell of ablated tissue surrounding the treatment volume(similar to the geometry of an eggshell surrounding an egg). Treating adesired tissue volume using this type of shell ablation has two primaryutilities in HIFU therapy: (1) In one embodiment, the ablated shellinterrupts the supply of blood to the interior of the treatment volume,causing the otherwise untreated tissue located within the shell toischemically necrose in situ. In this manner, the ischemic damage to thecenter of the volume results in the destruction of the entire volumeover time, even though only the outer boundary is directly treated withHIFU. (2) In another embodiment, the elemental treatment volumescomprising the shell pattern are deposited in such a way that heatconduction toward the interior of the volume results in immediatethermal destruction of the inner tissue, even though only the outerboundary is directly ablated with HIFU energy. Both of these utilitiesprovided by shell ablation serve to significantly improve the efficiencyof HIFU therapy because they result in an effective tissue treatmentvolume that is larger than the volume directed ablated with HIFU energy.Leveraging either or both of these shell ablation advantages increasesthe throughput achieved by a given HIFU procedure.

In another embodiment, a number of elemental treatment volumes arecreated to fill or partially fill the target treatment volume. With thistechnique, a greater percentage of tissue within the treatment volume isdirectly necrosed by exposure to the ablating energy than is the casewhen only the outer boundary is ablated.

In another embodiment, a HIFU treatment device directs a focal zone of aHIFU transducer to move in a path to surround or envelop a tissuevolume. The pattern in which the focal zone of the HIFU transducer ismoved results in creating a series of ablated tissue toroids of varyingdiameter that are stacked to surround and envelop the tissue volume. Inyet another embodiment, the focal zone is moved to create a spiral shellof ablated tissue to envelop the treatment volume.

In order to minimize treatment time and required user skill, oneembodiment employs a computer-controlled mechanism to automatically movethe HIFU focal zone and apply HIFU energy in such a manner to create thedesired geometric shell while the user simply holds the applicatorstationary.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features ofthe claimed subject matter, nor is it intended to be used as an aid indetermining the scope of the claimed subject matter.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thistechnology will become more readily appreciated by reference to thefollowing detailed description, when taken in conjunction with theaccompanying drawings, wherein:

FIG. 1A shows an internal tissue volume to be surrounded with an ablatedshell in accordance with one embodiment of the disclosed technology;

FIG. 1B is a detailed view of tissue inside and outside of the ablatedshell;

FIG. 2 illustrates an ultrasound image of a uterine fibroid tumor to betreated;

FIGS. 3A and 3B illustrate a cylindrical elemental treatment volumecreated in accordance with an embodiment of the disclosed technology;

FIG. 3C illustrates a relationship between safety and therapeutic rangeversus applied power of a HIFU signal;

FIG. 3D illustrates the side and top views of an elemental treatmentvolume that is created in accordance with one embodiment of thedisclosed technology, as well as the completely filled-in ablationvolume produced by this embodiment;

FIG. 3E illustrates the side and top views of a smaller elementaltreatment volume that is created in accordance with another embodimentof the disclosed technology, as well as the completely filled-inablation volume produced by this embodiment;

FIG. 3F illustrates the side and top views of a larger elementaltreatment volume that is created in accordance with another embodimentof the disclosed technology, as well as the partially filled-in ablationvolume produced by this embodiment;

FIG. 3G illustrates the uneven profile of treated tissue created by theapplication of energy in a single pass of the HIFU focus along thetissue volume;

FIG. 3H illustrates the more even profile of treated tissue created bythe application of energy in multiple passes of the HIFU focus along thetissue volume;

FIG. 3I illustrates creating an arc or segment elemental treatmentvolume by directing a focal zone back and forth over a portion of theperimeter of the total treatment volume desired;

FIGS. 3J and 3K illustrate a technique for creating an ablated shellaround a tissue volume from a number of elemental treatment volumes inaccordance with an embodiment of the disclosed technology;

FIGS. 4A and 4B illustrate a second technique for creating an ablatedshell around a tissue volume in accordance with another embodiment ofthe disclosed technology;

FIG. 4C illustrates a third technique for creating an ablated shellaround a tissue volume in accordance with another embodiment of thedisclosed technology;

FIG. 4D illustrates a technique for creating an ablated shell around auterine fibroid, which overlaps at least a portion of the adjacentendometrium, so as to further reduce menorrhagia symptoms;

FIG. 5 illustrates a HIFU treatment device in accordance with oneembodiment of the disclosed technology;

FIG. 6 illustrates one mechanism for varying a position and orientationof a focal zone of a HIFU transducer in accordance with one embodimentof the disclosed technology;

FIGS. 6A and 6B illustrate how the angular orientation of the focal zoneis changed with the mechanism shown in FIG. 6;

FIGS. 6C and 6D illustrate another mechanism for changing the depth andposition of the focal zone;

FIG. 7 illustrates a system for treating tissues with HIFU in accordancewith an embodiment of the disclosed technology; and

FIG. 8 illustrates two different HIFU signal waveforms.

DETAILED DESCRIPTION

As indicated above, the technology disclosed herein relates to a methodof treating internal body tissues such as uterine fibroids, benign ormalignant tumors, or the like. Although the following description isdirected to the use of the technology to treat uterine fibroids, it willbe appreciated by those of skill in the art that the technology can beused to treat a volume of any internal body tissue. In one embodiment,the desired treatment volume is treated by creating a pattern of one ormore elemental treatment volumes in the tissue. Though the technologydisclosed herein describes several possible geometries for theseelemental treatment volumes, each type of elemental volume shares thecommon feature that it is comprised of a volume of ablated tissue thatis greater than the volume of the HIFU focal zone due to controlledmotion of that focal zone around or along the elemental volume in aprescribed manner. The acoustic focal zone referenced herein is commonlydefined as the volume encompassed by the −6 dB pressure contour of theacoustic waveform as measured from its spatial maximum. Those skilled inthe art will recognize that the dimensions of this −6 dB pressurecontour are also referred to as the full-width half-maximum, or FWHM,dimensions. A typical focal zone as implemented in the embodimentsdescribed herein is ovoid in shape, with FWHM dimensions ofapproximately 10 mm. in length along the beam axis and 2 mm. in widthperpendicular to the beam axis.

In accordance with an embodiment of the disclosed technology, a desiredvolume of tissue to be treated is exposed to energy that ablates thetissue in a shell-like pattern, which completely or partially surroundsthe tissue volume while only directly ablating the outer boundary. Thetissue encompassed by the shell then remains in the body and necroses insitu due to effects other than direct ablation. These other effectscausing in situ necrosis may include some combination of:

-   -   1. ischemic necrosis, resulting from partial or complete        isolation of an encapsulated region from a surrounding blood        supply;    -   2. indirect thermal necrosis, resulting from inward thermal        conduction occurring during the creation of the ablated shell;        and/or    -   3. secondary injury due to normal healing processes        (inflammation, apoptosis, etc.).        The necrosed tissue located inside the ablated shell of the        treated volume is subsequently resorbed and/or healed by normal        body mechanisms.

FIG. 1A illustrates a tissue volume, such as a uterine fibroid 20, to betreated. Uterine fibroids may be irregularly shaped but are oftengenerally spherical or oval shaped. The fibroid 20 includes one or moreblood vessels 22 that supply the fibroid 20 with blood. In order totreat the fibroid 20, a 3-dimensional ablated shell 30 is formed insidethe periphery of the fibroid 20 in a manner that isolates the fibroidtissue inside the shell from the blood vessels 22 that supply blood to,and take blood from the fibroid 20. By cutting off the interior tissuefrom its blood supply with the ablated shell 30, this interior tissuecan be left in the body to ischemically necrose and eventually beabsorbed or healed via normal body healing mechanisms over a period ofdays/weeks.

In one embodiment, an ablated shell 30 is created by exposing the tissuesituated in the shell to HIFU energy for a sufficient time or atsufficient power so as to cause direct tissue necrosis. This is to bedistinguished from secondary ischemic necrosis that occurs in the tissueinside the shell as a result of it being cut off from its blood supplyor as a result of other effects listed above. Because the volume oftissue ablated to create the shell is smaller than the overall volume oftissue to be treated, the time required to treat the combined mass oftissue (i.e. shell plus encapsulated volume) is reduced below that whichwould be required if the entire volume were to be directly ablated. Asused herein, the term “ablation” refers to the direct necrosis of tissueresulting from the immediate thermal and/or mechanical effects caused byexposure of the tissue to the energy source. Also as used herein, theterm “shell” refers to an ablated surface which reduces or eliminatesblood flow across that surface. The geometry of this surface may be suchthat it entirely encapsulates a volume (e.g., a sphere) or non-closedsuch that it only partially encapsulates the volume (e.g., a concavedisk). The term “encapsulate” refers to creation of such surfaces.

In FIG. 1A, the shell 30 is shown as fitting entirely within volume ofthe fibroid 20. However, the size of the shell may be varied so that itsinner non-ablated region encapsulates the entire fibroid 20.Alternatively, the fibroid 20 may have multiple shells created therein.

In another embodiment, one or more partial shells are created which donot entirely encapsulate the tissue site, but reduce or eliminate bloodflow to or from its interior across those partial shell(s). This leadsto necrosis of at least part of the tissue volume.

FIG. 1B illustrates a close-up view of the interior of the fibroid 20and the ablated shell 30 that surrounds it. As indicated above, thefibroid 20 includes an interior region 25 within the ablated shell 30that will ischemically necrose by virtue of the tissue being cut offfrom an external blood supply (with some contributions via othersecondary injury pathway mechanisms associated with healing, e.g.,inflammation, apoptosis, et. al.). Tissue that forms the ablated shell30 is directly necrosed via thermal and/or mechanical effects ofexposure to the focal zone of the HIFU beam. Some fibroid tissue 35external to the ablated shell 30 may also be partially or completelydestroyed via thermal necrosis (due to heat conducted from the ablatedshell 30) and/or secondary injury pathway mechanisms (ischemia,inflammation, apoptosis, et. al.).

FIG. 2 illustrates a 2-dimensional image of a fibroid 20 produced withan ultrasound imaging transducer and other ultrasound imagingcomponents. As will be explained in further detail below, in oneembodiment, an imaging transducer and HIFU transducer are combined as asingle unit. In one embodiment, an ultrasound imaging transducer,ultrasound image processor and display (all not shown) are used toproduce the image of the fibroid 20 for a physician. The display mayinclude a crosshair or other marker 38 on the image of the fibroid 20that indicates a reference point with respect to the focal zone of theHIFU transducer so that a user can aim the HIFU transducer at the tissuevolume. The physician can interact with the display by, for example,adjusting the radius of a circular marker ring 40 that is centeredaround the crosshair 38 in order to specify the boundaries of thedesired treatment volume or the boundaries of the ablated shell to becreated (which may be the same). From the boundaries defined by the sizeof the marker ring 40, a processing system, such as general or specialpurpose computer (not shown) computes the size of the ablated shell thatshould be created to encapsulate the fibroid 20. In some embodiments,the marker ring 40 may be adjustable to form shapes other than a circle,such as ovals or cones, etc., by, for example, stretching the sides ofthe marker ring 40 in order to allow the physician to define the shapeof the three-dimensional ablated shell. In one embodiment, the size ofthe marker ring 40 is adjusted manually by the physician. In anotherembodiment, image processing techniques may be used to automaticallysize the marker ring based on an estimate of the boundaries of thetissue to be treated. The boundaries may be further adjusted by thephysician if desired. In some embodiments, the boundaries may beadjusted on a three-dimensional image of the tissue. Once the size ofthe size of the shell to be created is determined, a computer with theHIFU treatment system begins controlling the position of the focal zoneof the HIFU transducer to ablate the tissue to create the shell.

FIGS. 3A and 3B illustrate one exemplary configuration of a cylindricalelemental treatment volume 80 that is used to build up the full desiredtreatment volume. The elemental treatment volume 80 is created bydirecting a focal zone 81 of a HIFU beam 83 around the perimeter of theelemental treatment volume. The focal zone 81 can be continuously movedaround the perimeter of the elemental treatment volume for one or moretimes while a HIFU transmitter continually transmits HIFU pulses untilthe perimeter of the elemental treatment volume 80 is sufficientlyablated. Alternatively, the focal zone 81 can be moved to discretepositions around the perimeter and the HIFU beam 83 pulsed on and off tofully ablate the different positions around the perimeter of theelemental treatment volume.

As shown in FIG. 3B, the elemental treatment volume 80 has a center area79 that is not directly or is minimally exposed to the focal zone 81 ofthe HIFU beam 83. This center area 79 is actively necrosed by heatconduction created as the perimeter of the elemental treatment volume isablated. In one particular preferred embodiment, the elemental treatmentvolume 80 has a diameter of approximately 11 mm. and a height ofapproximately 10 mm., thereby producing a volume of approximately 1 cc.In this particular preferred embodiment, the volume of the elementaltreatment volume is therefore approximately 40 times greater than thevolume of the focal zone. Heat from the ablation of the perimeter of theelemental treatment volume is conducted inwards as indicated by thearrows 67 in order to treat the center area 79. At the exterior of theelemental treatment volume, the heat is dissipated outwards as indicatedby the arrows 69.

FIG. 3C conceptualizes the effect of the applied HIFU power level on theresultant therapeutic range and safety margin of a HIFU treatmentregimen. With conventional techniques that do not combine the effects ofthe technology disclosed herein, the range of acoustic power levelswhere a treatment regimen is both effective and safe can be relativelynarrow, as indicated by range “a”. That is, small changes to the HIFUpower that result in it falling outside the narrow region “a” make thetreatment ineffective or possibly unsafe. However, by treating thetarget tissue using a combined set of effects including one or more ofthe following (1) focal scanning to produce elemental treatment volumes,(2) inward heat conduction within an elemental volume, and (3) spatialspecificity resulting from the application of highly nonlinear acousticenergy with a moderately low fundamental frequency, it is believed thatthe range of safe and efficacious HIFU power levels can be increased, asindicated by range “b,” such that the treatment method is not assensitive to changes in HIFU power delivered. These various effectsacting synergistically to improve HIFU treatment efficiency andcollateral tissue safety will be more fully described below.

The size of the elemental treatment volumes can be varied as a functionof a variety of factors including the geometry of the devices that willapply the treatment energy. In the embodiment shown in FIG. 3D, anelemental treatment volume 80 is shown in top and side views. Thiselemental treatment volume is generally cylindrical with a width W andlength L that are both approximately equal to the length of the focalzone of the HIFU transducer. As the focal zone is moved around theperimeter of the elemental treatment volume with velocity V, the entirecross-section 80 a of the elemental treatment volume is treated due toeither direct exposure to the HIFU beam or indirect thermal necrosiscaused by inward conduction of heat from the treated perimeter.

FIG. 3E shows top and side views of a smaller elemental treatment volume85 having a diameter that is approximately twice the diameter of thefocal zone. With this embodiment, the elemental treatment volume stillhas well defined boundaries due to the motion of the focal zone aroundthe perimeter of the elemental treatment volume as it is being created.The elemental treatment volume has a cross section 85 a that isgenerally uniformly treated all the way through the interior of thevolume. The disadvantage of this elemental treatment volume 85 is thatit is small compared with the elemental treatment volume shown in FIG.3D, and therefore more elemental treatment volumes may be required totreat a desired tissue site.

FIG. 3F shows top and side views of yet another elemental treatmentvolume 89 having a diameter that is significantly larger than the focalzone of the HIFU transducer. In this case, cooperative heating of theinterior of the elemental treatment volume does not occur and only theperimeter 89 c of the elemental treatment volume is ablated. As aresult, the interior may not be treated, as depicted by the open centerwithin the ablated ring. While the geometry of the elemental treatmentvolume 89 is not currently preferred for creating the building blocksused to treat a volume of tissue, the geometry may be useful in creatingablated shells around tissue treatment sites as will be discussed infurther detail below. In yet another embodiment, the building blocks(elemental treatment volumes) may be formed of linear segments createdby passing the beam for a number of times along their length.

FIG. 3G illustrates a scenario in which the entire dose of treatmentenergy is applied to the tissue in a single pass of the HIFU focal zonealong or around the elemental volume. Rapid deposition of energy in thismanner can result in the formation of large pre-focal bubbles in thetissue that reflect the treatment energy, therefore preventing evenablation at all depths along or around the elemental volume. As aresult, an uneven or “ragged” treatment pattern 91 a is created, havingdifferent depths of treated tissue. In contrast, by distributing thedose of treatment energy over a series of passes along or around theelemental volume, a more even and uniform treatment pattern 91 b iscreated, such as shown in FIG. 3H. On each pass, a portion of theelemental treatment volume is ablated and the elemental treatment beginsto build up. The multi-pass technique is used in the creation of theelemental treatment volumes described below.

FIG. 3I illustrates a technique for creating another embodiment of anelemental treatment volume with an arc or segment-type geometry. Thiselemental treatment volume can be used to create rings or other shapeswith uniform treatment depths and in one method to form a shell aroundthe desired treatment volume. In this embodiment, the focal zone of theHIFU transducer is moved back and forth over a portion (e.g. an arc) ofthe perimeter. The back-and-forth motion of the HIFU focus results intissue ablation at uniform depths because it distributes the acousticenergy over a broader region during the treatment, therefore preventingthe formation of large pre-focal bubbles that can reflect energy andresult in uneven or “ragged” treatment patterns. Multiple treated arcscan therefore be created side by side to complete the treated perimeterof the desired treatment volume.

In each of the examples shown in FIGS. 3A-3B, 3D-3I, the elementaltreatment volumes have a height or length that is approximately the sameas the focal zone of the HIFU transducer. In some embodiments, theheight of an elemental treatment volume may be increased by varying thedepth of the focal zone during the application of treatment energy.

In one embodiment described in further detail below, the focal zone 81of the HIFU beam 83 is steered over the perimeter of the cylindricalelemental treatment volume 80 with a mechanical wobbler at a rate thatacts to largely confine the heat within the center 79 of the treatmentvolume as the elemental treatment volume is being created. The focalzone of the HIFU signal is directed around the perimeter of theelemental treatment volume in such a manner that the interior of thetreatment volume is ablated by inward thermal conduction, but the energydeposited beyond its exterior boundary remains below the thresholdrequired for inciting thermal or mechanical damage. Alternatively, thefocal zone 81 of the HIFU beam 83 can be steered around the perimeter ofthe elemental treatment volume with electronic beam steering.

To create the elemental treatment volumes described herein, asubstantially non-linear, pulsed waveform of HIFU energy, such as thewaveform 230 shown in FIG. 8 is applied to the perimeter of theelemental treatment volume. The currently preferred embodiment of thiselemental unit volume technique relies on the HIFU treatment waveformbeing substantially nonlinear in nature, meaning that the originallysinusoidal characteristic of the incident waveform is heavily distortedby the time it reaches the HIFU focus. The presence of nonlinearity inthe focal acoustic waveform is indicative of the conversion of energyfrom the fundamental acoustic frequency into higher harmonics, which inturn are more readily absorbed by the tissue residing in and immediatelyadjacent to the focal zone. This effect results in a dramaticallyincreased heating rate that remains tightly localized to the focalregion, leading to increased treatment efficacy while maintaining thesafety of collateral tissues. The degree of focal waveform nonlinearityrequired in this preferred embodiment ranges from moderate distortion,where the compressional pressure is perhaps twice that of therarefactional pressure, to severe distortion reaching the point of shockformation, where the compressional pressure can be more than five timesgreater than the rarefactional pressure.

In one particular experimental construct, the peak acoustic powers usedto attain the desired level of nonlinearity in the HIFU focal zone rangefrom 800-1700 watts, depending upon the depth of the particularelemental tissue volume with respect to the body surface. These acousticpowers are delivered to the elemental volume in a pulsed fashion, wherepulses consist of 15-30 cycles at a nominal operating frequency of 1 MHzand are delivered at pulse repetition frequencies (PRFs) of 4-8 kHz,resulting in a pulsing duty factor of approximately 10%. This pulsingduty factor is reduced to an overall duty factor of approximately 5%through the use of interleaved ultrasound imaging during the HIFUtreatment (as described in U.S. Pat. No. 6,425,867, which is hereinincorporated by reference). While the HIFU transmitter is applyingenergy of these specifications, a cylindrical elemental treatment volumeis created by mechanically wobbling the HIFU focus, which isapproximately 10 mm. in length and 2 mm. in width in FWHM dimensions,around a 10-mm-diameter trajectory at a rate of approximately 2 Hz. Inthis case, the diameter around which the HIFU focus rotates isapproximately equal to the HIFU focal zone length and five-fold greaterthan the HIFU focal zone width. The mechanical wobbling and HIFUtreatment continue for a total time of 10-50 seconds per elementalvolume, depending on the depth in the tissue where the elemental volumeis located and the overall tissue treatment volume desired.

Although the currently preferred embodiment uses a non-linear pulsedwaveform, it will be appreciated that a continuous-wave (CW) or linearHIFU signal such as the waveform 232 shown in FIG. 8 may also be useddepending on the power level used and the rate at which the focal zoneis moved.

Though this previous example specifies the use of a 2 Hz mechanicalrotation rate around the perimeter of the elemental volume, both lowerand higher rates could be used to ablate these types of elementalvolumes. However, if too low a rate is used, the heat that ablates theperimeter of the elemental treatment volume may not be sufficientlycontained within the interior of the elemental volume and may result inadverse effects in collateral tissues. Higher rotation rates may requirethe use of an electronic beam former instead of mechanical rotation andmay also affect the HIFU treatment power necessary. In one embodiment,the mechanical rotation rate of the HIFU focus about the unit volumediameter is at least 0.25 Hz. In another more preferred embodiment, thisrotation rate is at least 1 Hz, while in the most preferred embodimentthis rate is at least 2 Hz. Regardless of the rotation rate used, it ispreferable to apply energy over a number of passes (e.g. two or more)around the perimeter at a rate and power level that allows the entireelemental treatment volume to be ablated in unison, in order to achievesymmetric geometry in the shape of the ablated elemental volume andprevent distortion to produce an evenly ablated tissue site.

As will be appreciated, the size of the elemental treatment volume ispreferably selected so that a center region 79 can be indirectly treatedwhile not unduly increasing the treatment time required to treat adesired volume of tissue. If the size of the elemental treatment volumeis too large, the center region 79 will not be ablated by effectiveconduction of heat into the interior of the volume. Conversely, if thesize of the elemental treatment volume is too small, then the timerequired to treat the desired treatment volume must be adjusted to avoidover-dosing the elemental volume and potentially causing damage tocollateral tissues. In addition, the time to create each elementaltreatment volume may decrease as the focal zone is moved proximallytoward the surface of the body, due to the residual heat persisting inthe treatment volume from ablation of the more distal elemental volumes.

Although the elemental treatment volume 80 shown in FIGS. 3A and 3B iscylindrical in shape, it will be appreciated that other shapes such asspherical or cubic elemental treatment volumes etc. could be createddepending on the steering capabilities of the HIFU beam 83.

In a currently preferred embodiment, the method of creating theelemental treatment volumes takes advantage of several features of HIFUtherapy resulting from the synergistic effects of highly-nonlinearacoustic waveforms and the mechanical or electronic motion of the HIFUfocus about the perimeter of the unit volume. These combined effectscomprise a set of operating points that result in the enhanced safetyand efficacy observed when using this treatment method. This set ofoperating points includes a combination of the following: (1) Theelemental treatment volume is ablated in such a way that the interiorregion is primarily destroyed through inward conduction of heat, notdirect ablation by HIFU. This feature enlarges the size of the elementalvolume without increasing the HIFU dose that has to be delivered to thetissue to do so. (2) The motion of the HIFU focal zone about theelemental treatment volume perimeter is accomplished by making multiplepasses around the perimeter using a specified rotation rate, as opposedto making one a single pass around the circumference of the unit volumeto achieve ablation. This feature allows the tissue within the elementaltreatment volume to be ablated with uniform, smooth boundaries and equallength at substantially all points around the perimeter. (3) Theelemental treatment volume is subjected to highly concentrated acousticenergy only in the focal region of the HIFU beam by virtue of the use ofa highly nonlinear acoustic waveform that dramatically enhances theheating rate in the focal zone. (4) The fundamental acoustic frequencyof the HIFU applicator is kept low enough to ensure safe propagationthrough collateral tissues proximal to the body surface.

FIGS. 3J and 3K illustrate one technique for using the elementaltreatment volumes 80 to treat a desired volume of tissue. In thisembodiment a three dimensional pattern of adjacent elemental treatmentvolumes are created such that together they form an ablated shell thatsurrounds all or a portion of a desired tissue treatment volume. In theembodiment shown in FIGS. 3J and 3K, an ablated shell 87 is formed froma number of smaller ablated elemental treatment volumes 80, 82, 84, 86,88 etc. Each of the elemental treatment volumes is created sufficientlyclose together to form a necrosed shell or barrier of ablated tissuebetween the encapsulated tissue and its blood supply. As shown, theelemental treatment volumes 80, 82, 84, 86, 88 etc. are created adjacentto each other in annular patterns of increasing internal diameter thatextend from the distal end of the desired tissue treatment volume toapproximately midway in the tissue volume, where the diameter of thetreatment volume is the largest. The diameter of the annular patternsthen progressively decreases towards the proximal end of the tissuevolume to be treated. Together the annular patterns create a shell witha “hollow” interior space 90 that encapsulates a portion of the desiredtissue volume to be treated. With the elemental treatment volumes placedsufficiently close to each other, blood supplied to the fibroid or othertissue to be treated is cut off, or is substantially reduced so that thetissue will ischemically necrose when left in the body. In addition,some or all of the tissue within the center of the shell may necrose dueto heat conduction when the shell is being created. Because the entiretreatment volume is not ablated, there is less possibility that excessheat will be created in the body which may damage untargeted tissue andthe treatment time is significantly reduced from that required if theentire volume were to be directly ablated.

Although the shell 87 illustrated in FIGS. 3J and 3K is shown as beinghollow, it will be appreciated that it in some circumstances it may bedesirable to create one or more elemental treatment volumes within theinterior of the shell to actively necrose some or all of the tissueinside the shell 87. The number and spacing of the elemental treatmentvolumes can be decided by the physician based on experience, the timeavailable for treatment, the type of tissue being treated or otherfactors. Alternatively, a processor can be programmed to determine ifthe interior of the shell should be empty or filled with one or moreelemental treatment volumes.

The shell 87 is shown in FIG. 3J as being substantially sealed about itsouter surface. However, it will be appreciated that a shell 87 can stillbe created even if there are gaps between the individual elementaltreatment volumes. How close the elemental treatment volumes are placedin order to create the shell may be based on the type of tissue beingtreated, the thermal conductivity of the tissue, its absorptioncharacteristics, or other factors.

As will be appreciated, other patterns besides shells of elementaltreatment volumes can be used to treat the desired tissue volume. Forexample, layers of horizontally spaced adjacent elemental treatmentvolumes can be created in the desired tissue volume. The distancebetween elemental treatment volumes in a layer can be closely spaced ormore spread apart.

FIGS. 4A-4B show an alternative technique for creating an ablated shell92 around a tissue volume in accordance with the disclosed technology.In this embodiment, an ablated shell comprises a stacked series oftoroids, each having a varying internal diameter. A toroid 94 of minimuminternal diameter (or a solid disk) is placed at the distal end of thetissue to be treated with respect to the HIFU transducer. Additionaltoroids are created proximally to the distal toroid 94, includingtoroids 95, 96, 98 of increasing diameter up to a toroid 100 where thetoroid has a maximum internal diameter. The internal diameters of thetoroids then get progressively smaller with toroids 102, 104, 106 as theHIFU focal zone is moved more proximally before closing the shell 92with a toroid 108 of minimum internal diameter (or a solid disk) at themost proximal location in the treatment volume. As can be seen in FIG.4B, the interior of each of the toroids 94-108, when stacked, define ashell with a “hollow” (i.e. un-ablated) region 110 that encapsulates avolume of the tissue to be treated and isolates it from its bloodsupply. In one embodiment, the outer diameter of the toroids 94-108 isselected to correspond to the outer dimension of the fibroid in order tominimize the volume of tissue that is directly ablated with HIFU. Inanother embodiment, the outer diameters of the toroids 92-106 areselected to be within a set distance internal to the fibroid's outerboundary in order to allow the fibroid tissue external to the ablatedshell 92 to be partially or completely destroyed via thermal necrosis(due to heat conducted from the ablated shell 92) and/or secondaryinjury pathway mechanisms (ischemia, inflammation, apoptosis, et. al.).In yet another embodiment, the inner diameters of the toroids 94-108correspond to the outer diameter of the tissue volume such that theinterior 110 of the ablated shell 92 created is slightly larger than thetissue volume, perhaps allowing a more complete kill of tumor tissue atthe expense of killing a small amount of surrounding healthy myometrium.Another advantage of such an embodiment is the ability to create theablated shell 92 such that it overlaps the endometrial lining, thusnecrosing at least some of the nearby endometrium which may reducemenorrhagia symptoms.

FIG. 4C shows yet another embodiment of an ablation pattern that createsan ablated shell to encapsulate a tissue volume and isolate it from anexternal blood supply. In the embodiment shown, an ablated shell iscreated from a spiral pattern 120. The spiral has a minimum diameter ata distal end 122 of the tissue volume to be treated, expands to amaximum diameter at approximately the mid point of the tissue volume,and then progressively decreases in diameter towards the proximal end124 of the tissue volume. Each loop of the spiral pattern 120 issufficiently close to an adjacent loop that the tissue is activelynecrosed in order to create an ablated shell around a tissue volume thatcuts off the tissue in the shell from its blood supply. As will beappreciated, the spiral pattern 120 could also be used to create thesmaller elemental treatment volumes described above and shown in FIGS.3A and 3B depending on the size of the focal zone of the HIFU transducerand the desired size of the elemental treatment volumes.

FIG. 4D illustrates a uterus having three different types of fibroidsincluding an intramural fibroid 130, a subserosal fibroid 132, and asubmucosal fibroid 134. In the example shown, an ablated shell 135 iscreated to encapsulate the entire submucosal fibroid 134 on one side ofthe uterine wall as well as a portion of the nearby endometrium tissue136 on the opposite uterine wall. By creating the ablated shell 135 toencapsulate not only the fibroid 134 but also a portion of the adjacentendometrium 136, menorrhagia symptoms may be reduced.

Although the shape of the ablated shells is shown as being generallyspherical in FIGS. 3J-3K, 4A-4B and 4C, it will be appreciated thatother shapes, such as conical or double conical, ovoid (e.g., eggshaped), or rectangular could be used. The particular shape of the shellcreated may depend on the shape of the tissue volume to be treated andthe ability of the equipment used to steer the focal zone of the HIFUtransducer in a desired pattern. Any shell shape of ablated tissue thatforms a barrier between tissue internal to the shell and its externalblood supply will function to allow the encapsulated tissue toischemically necrose when left in the body. It will also be appreciatedthat, as an alternative to ablating an excessively large or irregularlyshaped shell, one could ablate two or more regularly-shaped shellsadjacent to each other to treat most or all of the desired volume (e.g.,2 spherical shells could be ablated side-by-side inside an oblong tumor,rather than ablating one oblong shell). If numerous shells are createdwithin the tissue volume, one can also form a matrix (or “honeycomb”) ofablated elemental tissue volumes with interspersed regions of un-ablatedtissue which subsequently ischemically necrose in situ. Such a matrixcould involve regular or random spacing of ablated elemental treatmentvolumes to accomplish the same effect, and the matrix could consist ofnumerous closed shells (e.g., spherical shells) or layers ofstacked/overlapping elemental treatment volumes.

Those skilled in the art will readily appreciate that other advantagesof the shell ablation approach are (1) increased treatment rate, sinceenergy is applied to a sub-volume of the tissue ultimately treated, (2)a larger treatment size for a given allotment of treatment time, (3) andless energy required, compared to that which would be used if the entirevolume including its interior were directly ablated. Automating a HIFUsystem to ablate a symmetrical (e.g., spherical) shell will reducedemands on a user with regard to imaging, targeting and probemanipulation. If shell is symmetrical, user can easily visualize itsprojected relationship to tumor boundaries as visualized with an imagingmechanism such as an ultrasound imager, MRI, x-ray, etc. The user needonly manipulate the HIFU system so as to center an overlay of theprojected shell within the image of the target tissue, expand thediameter of the shell to desired dimensions (e.g., just inside peripheryof the tumor), and then hold the system stationary while the systemautomatically ablates the specified shell pattern.

FIG. 5 shows one embodiment of a HIFU treatment device that can be usedto treat tissue in the manner described above. The HIFU treatment device150 is a hand held or hand guided applicator device that includes animaging transducer 152 and a HIFU transducer 154. The imaging transducer152 is fixed in position to capture images of tissue within a body thatincludes the focal zone of the HIFU transducer 154. As will be explainedin further detail below, the focal zone of the HIFU transducer 154 canbe mechanically and/or electrically steered to ablate a number ofelemental treatment volumes that are adjacently positioned to create ashell that surrounds or encapsulates a desired tissue volume or tocreate another pattern. While holding the treatment device 150 steady atthe desired location, as determined from an image produced from signalsobtained from the imaging transducer 152, the focal zone of the HIFUtransducer 154 is moved in such a way as to ablate a pattern ofelemental treatment volumes in order to create a shell around thetreatment volume or to create another pattern of elemental treatmentvolumes.

The treatment device 150 is coupleable to other components of thetreatment system including an image processor and display required tooperate the imaging transducer 152 and produce images of the tissuevolume. A signal source required to drive the HIFU transducer and acomputer to orient the focal zone of the HIFU transducer in a pattern tocreate the elemental treatment volumes in a desired pattern such as ashell around the tissue volume are also included.

FIG. 6 illustrates one embodiment of a more detailed mechanism fortreating the internal body tissues with HIFU signals to create a seriesof elemental treatment volumes in a shell or other pattern. Thetreatment device 150 includes a HIFU transducer 154. In the embodimentshown, the HIFU transducer 154 has a fixed focal zone, as defined by thecurvature of the piezoelectric elements that comprise the transducerhead. A flexible membrane that does not significantly reflect HIFUsignals is positioned in front of the HIFU transducer to form a chamberin which liquid can be introduced, stored, and/or circulated. A liquidsuch as water or de-gassed water then fills the liquid chamber andsurrounds the transducer 154 to serve as an acoustic couplant to thetissue. A port 156 connects the treatment device to a pump to allow theliquid of a constant volume to flow around the HIFU transducer.

To adjust the depth of the focal zone where the HIFU signals aredelivered to the patient, a linear actuator 160 or motor raises orlowers the HIFU transducer 154 within a housing of the treatment device150 via a threaded rod or other mechanism. By adjusting the height ofthe transducer 154 within the housing, the depth where the HIFU signalsare delivered within the body can be controlled.

In addition, the treatment device 150 includes an offset bearing 170that, when rotated by a motor 168, wobbles an end of a shaft 172 aroundthe center of the offset bearing 170. The HIFU transducer 154 is coupledto the other end of the shaft 172 through a slidable bearing. A linearactuator 164 or motor positions a spherical bearing 174 that surroundsthe shaft 172 towards or away from the offset bearing 170. The positionof the spherical bearing 174 on the shaft 172 controls the angularorientation of the focal zone of the HIFU transducer 154.

As shown in FIGS. 6A and 6B, by turning the shaft of the motor 168 andby changing the angular orientation of the focal zone of the HIFUtransducer by adjusting the position of the spherical bearing 174 alongthe length of the shaft 172, toroidal rings of ablated tissue or annularpatterns composed of ablated cylinders/spheres can be created in thebody at various depths.

If the motors 164 and 168 are simultaneous rotated back and forththrough a desired angle with signals that are approximately 90 degreesout of phase, the focal zone of the HIFU transducer will trace out asubstantially circular pattern off a central axis of the treatmentdevice 150, thereby allowing the creation of an elemental treatmentvolume at a desired location in the body as shown in FIG. 6B. Bycontinuously rotating the motor 168 while the spherical bearing 174 isat the farthest point from the motor 168, the elemental treatment volumecan be created at the top and bottom of the shell depending on the depthof the focal zone.

In one embodiment, to treat a desired tissue volume, a physician obtainsan image of the tissue volume with the imaging transducer 152 andadjusts the radius of a marker ring on the image or interacts with someother graphical user interface or keyboard to define the boundaries ofthe desired shell. Based on the radius of the marker ring, a computercalculates the volume or shape of the ablated shell to be created in thebody. The HIFU transducer and motors within the treatment device 150 arethen activated such that a pattern of elemental treatment volumes isablated to form the shell that surrounds or encapsulates the tissuevolume or some other desired pattern of elemental treatment volumes.When creating elemental treatment volumes, the focal zone of the HIFUtransducer may be continually moved until a treatment volume is ablatedor the focal zone may be moved to discrete positions around theperimeter of the elemental treatment volumes and a HIFU signal appliedto create the elemental treatment volumes.

In another embodiment, the linear actuator 160 that adjusts the focalzone depth, the linear actuator 164 that adjusts the angle of the HIFUtransducer, and the motor 168 that rotates the shaft 172 aresimultaneously operated to create a spiral shell ablation pattern of thetype shown in FIG. 4C.

Following treatment, the patient may be injected with a contrast agentto allow the physician to confirm that blood perfusion has beenappropriately reduced or eliminated within the targeted tissue volume.Non-perfusion would provide a strong indication that the treated tissuevolume will undergo (or has undergone) ischemic necrosis. Such contrastagents are well known in the art for use with various different imagingmodalities including ultrasound, MRI, x-ray, CT, etc.

As will be appreciated, other mechanisms are possible to selectivelyposition the focal zone of a HIFU transducer to create the elementaltreatment volumes and treat the desired tissue volume. FIGS. 6C AND 6Dillustrate another alternative embodiment where a transducer 180 ismoved in two orthogonal directions (x,y) by a pair of linear actuators182, 184. The linear actuators, which could be motors that drive a wormgear or other mechanisms, are computer controlled so that the positionof the focal zone of the HIFU transducer 180 is moved as desired. Athird motor or actuator (not shown) can be computer controlled to varythe height of the transducer 180 to change the depth of the focal zone.

FIG. 7 illustrates a basic block diagram of a HIFU ultrasound treatmentsystem in accordance with one embodiment of the disclosed technology. Inthis embodiment, a patient treatment device includes both a HIFUtransducer 154 and an ultrasound imaging transducer 152. The transducersmay be separate devices as shown in FIG. 6 or may be an integrateddevice with HIFU and imaging ultrasound elements located on the sametransducer head. Controlling the operation of the imaging and HIFUtransducers is a system controller 200 that may include one or moregeneral purpose or special purpose programmed processors that areprogrammed to perform the functions described herein. The systemcontroller 200 supplies control signals to a HIFU control unit 202 thatselects the power of the HIFU signals to be provided by the HIFUtransducer 154.

In one embodiment, the operating power level is selected by transmittinga number of test signals at different power levels and analyzing theecho signals created in response to the transmitted test signals. Theoperating power level for HIFU treatment is selected when a desiredcharacteristic of an echo signal, such as a ratio of the power ofdifferent frequency components within the echo signal, begins tosaturate. In one embodiment, the operating power selected is that whichcauses the power of the second harmonic signal to saturate irrespectiveof further increases in the power of the fundamental frequency of theHIFU signal. Further detail of possible methods of selecting andcontrolling the HIFU power can be found in U.S. patent application Ser.No. 12/537,217 filed Aug. 6, 2009 and which is herein incorporated byreference.

The imaging transducer 152 is controlled by an imaging ultrasoundcontroller 204 that includes conventional ultrasound components such asa transmit/receive switch, beam former, RF amplifiers and signalprocessors. The output of the ultrasound controller 204 is fed to anultrasound signal processor 210 that operates to produce ultrasoundimaging signals for display on a video monitor 212 or other display. Theimage signals can also be stored on a computer readable media (DVD etc,video tape), printed by a printer or otherwise stored for laterdiagnosis or analysis.

A computer controlled steerer 205 is controlled by the system controller200 to create a number of elemental treatment volumes to treat a desiredvolume of tissue. In one embodiment, the computer controlled steerer 205mechanically adjusts the angular orientation or x,y position of the HIFUtransducer 154 and the depth of the focal zone to direct the HIFU energyat a desired location. In another embodiment, the computer controlledsteerer 205 electronically adjusts the angular orientation or x,yposition of the focal zone of the HIFU transducer 154 and the depth ofthe focal zone of the HIFU transducer 154 to create the elementaltreatment volumes.

A footswitch 214 allows a physician or their assistant to selectivelydeliver HIFU energy to the patient in order to treat a tissue site. Inaddition, the physician can manually change the size and shape of thetreatment volume and other functions of the system using one or morecontrols on a control panel 216.

In some embodiments, the system may include an image position control220 that changes the orientation of the imaging transducer 152 so thatthe physician can view the desired target tissue volume to be treated atdifferent angles or in different planes. The image position control beeither mechanical or electronic and is controlled by the systemcontroller 200.

While illustrative embodiments have been illustrated and described, itwill be appreciated that various changes can be made therein withoutdeparting from the scope of the invention. For example, although theenergy source used to create the ablated shell is HIFU in the disclosedembodiments, other energy sources could be used such as radiation,lasers, rf, microwaves, cryoablation, etc. Some of these energy sourcesare minimally invasive such that they must be delivered to the tissuevolume with a catheter, endoscope, or the like. Applying energy fromthese energy sources ablates the perimeter of the tissue volume tocreate an ablated shell. In another embodiment, the HIFU transducer maybe insertable in to the body such as transvaginally or rectally. If thetissue volumes to be treated can be seen from the location of the HIFUtransducer, then images of the tissue can be obtained with image sensorsother than ultrasound image sensors. In some embodiments, the imaging ofthe desired treatment volume may be done with another type of imagingmodality such as MRI, x-ray, infrared, or the like in a manner thatallows a physician to confirm that the HIFU is being delivered to thearea of desired target tissue volume. Therefore, the scope of theinvention is to be determined from the following claims and equivalentsthereof.

1. A system for treating a desired treatment volume of tissue with highintensity focused ultrasound (HIFU), comprising: a HIFU transducerconfigured to deliver treatment energy to a focal zone; and a processorprogrammed to repeatedly position the focal zone over a perimeter of oralong an elemental treatment volume as treatment energy is applied. 2.The system of claim 1, wherein the elemental treatment volume has sizeselected such that an interior region is treated by indirect heating asthe treatment energy is applied to the perimeter of the elementaltreatment volume.
 3. The system of claim 1, wherein the processor isprogrammed to position the focal zone of the HIFU transducer in apattern to create a number of elemental treatment volumes within thedesired treatment volume.
 4. The system of claim 1, wherein theprocessor is programmed to position the focal zone of the HIFUtransducer in a pattern to create a shell of elemental treatment volumesaround the desired treatment volume of tissue.
 5. The system of claim 4,wherein the processor is programmed to position the focal zone of theHIFU transducer to create the shell of elemental treatment volumesaround a tumor or uterine fibroid in a body.
 6. The system of claim 1,wherein the treatment energy is non-linear at the focal zone.
 7. Thesystem of claim 1, wherein the elemental treatment volume is cylindricaland has a diameter approximately equal to a length of the focal zone. 8.The system of claim 1, wherein the processor is programmed to control amechanical linkage that adjusts the position of the HIFU transducer. 9.The system of claim 1, wherein the processor is programmed to control anelectronic beam steerer.
 10. The system of claim 1, wherein theprocessor is programmed to position the focal zone of the HIFUtransducer around the perimeter of the elemental treatment volume andcontrol the application of treatment energy such that the tissue of theelemental treatment volume is partially ablated with each pass of thefocal zone around the perimeter of the elemental treatment volume.
 11. Asystem for treating a desired treatment volume of tissue with highintensity focused ultrasound (HIFU), comprising: a HIFU transducerconfigured to deliver treatment energy to a focal zone; and means forcreating one or more elemental treatment volumes within the desiredtreatment volume of tissue by repeatedly positioning the focal zone ofthe HIFU transducer around a perimeter of the elemental treatment volumeas treatment energy is being delivered such that the perimeter isdirectly treated by the treatment energy and an interior region of theelemental treatment volume is indirectly treated.
 12. The system ofclaim 11, wherein each elemental treatment volume is a cylinder having adiameter substantially equal to a length of the focal zone.
 13. Thesystem of claim 11, wherein each elemental treatment volume is acylinder having a diameter that is larger than twice the diameter of thefocal zone.
 14. The system of claim 13, wherein each elemental treatmentvolume has a height substantially equal to the length of the focal zone.15. The system of claim 11, wherein the means for creating the one ormore elemental treatment volumes includes a mechanical linkage to movethe transducer such that the focal zone is repeatedly positioned aroundthe perimeter of the elemental treatment volume.
 16. The system of claim11, wherein the means for creating the one or more elemental treatmentvolume includes an electronic beam steerer that electronically orientsthe focal zone of the HIFU transducer such that the focal zone isrepeatedly positioned around the perimeter of the elemental treatmentvolume.
 17. The system of claim 11, wherein the means for creating oneor more elemental treatment volumes creates a pattern of elementaltreatment volumes within the desired treatment volume of tissue.
 18. Thesystem of claim 17, wherein the pattern of elemental treatment volumesdefines a shell that encompasses a portion of the desired treatmentvolume of tissue.
 19. The system of claim 18, wherein the shellencompasses a tumor in a body.
 20. The system of claim 18, wherein theshell encompasses a uterine fibroid in a body
 21. The system of claim11, wherein the treatment energy is a HIFU signal that is non-linear intissue at the focal zone.
 22. A method of operating a HIFU ultrasounddevice to treat a desired tissue volume, comprising: selectivelycontrolling the position of a focal zone of a HIFU transducer such thatthe focal zone is repeatedly positioned around a perimeter of anelemental treatment volume; and applying treatment energy to the tissuewhile the focal zone is oriented at a number of positions around theperimeter of the elemental treatment volume such that the perimeter isrepeatedly ablated by direct exposure to the treatment energy and aninterior of the elemental treatment volume is indirectly treated by heatdue to the direct ablation of the perimeter of the elemental treatmentvolume.
 23. The method of claim 22, further comprising selectivelycontrolling the focal zone of the HIFU transducer to create a pattern ofelemental treatment volumes within the desired tissue volume.
 24. Themethod of claim 23, wherein the pattern of elemental treatment volumesdefines a shell that partially or completely encapsulates the desiredtissue volume.
 25. The method of claim 24, wherein position of the focalzone is controlled to create a pattern of elemental treatment volumesthat are sufficiently close together to form the shell.
 26. The methodof claim 22, wherein the focal zone of the HIFU transducer isselectively positioned over a diameter that is approximately equal to alength of the focal zone to create each elemental treatment volume. 27.The method of claim 24, further comprising selectively controlling thefocal zone of the HIFU transducer to create two or more shells withinthe desired tissue volume.
 28. The method of claim 22, wherein applyingthe treatment energy includes delivering HIFU signals that arenon-linear at the focal zone to the tissue.
 29. The method of claim 22,further comprising: producing an image of the desired tissue volume;displaying the image of the tissue on a video display screen; receivinginput from a user that indicates a boundary of the desired tissuevolume; and determining a required pattern for moving the focal zone tocreate a number of adjacent elemental treatment volumes to form anablated shell which encapsulates some or all of the desired tissuevolume, based on the input from the user.
 30. The method of claim 22,wherein the focal zone of the HIFU transducer is positioned around theperimeter of the elemental treatment volume and treatment energy isapplied such that the tissue of the elemental treatment volume ispartially ablated with each pass of the focal zone around the perimeterof the elemental treatment volume.
 31. The method of claim 22, whereinthe treatment energy is a pulsed HIFU signal.
 32. The method of claim24, wherein the shell is created to encompass all or a portion of atumor or uterine fibroid.
 33. A system for treating a tumor or uterinefibroid within a body with high intensity focused ultrasound (HIFU),comprising: a HIFU transducer configured to deliver treatment energy ina controllable direction to a focal zone; and a processor programmed todirect the focal zone as treatment energy is applied to create anablated shell that encompasses all or a portion of the tumor or uterinefibroid.
 34. The system of claim 33, wherein the processor is programmedto direct the focal zone in pattern that forms the shell from a numberof elemental treatment volumes.
 35. The system of claim 34, wherein theprocessor is programmed to repeatedly direct the focal zone on theperimeter of each elemental treatment volume.
 36. The system of claim33, wherein the processor is programmed to direct the focal zone inpattern of annular rings that are stacked to encompass all or a portionof the tumor or uterine fibroid.